Anti-microbial carpet underlay and method of making

ABSTRACT

A method for making antimicrobial rebonded carpet pad includes mixing zinc pyrithione with a polyol to form an antimicrobial polyol mixture concentrate, blending the antimicrobial polyol mixture concentrate with a binder stream, mixing the binder with foam particles and curing the binder. The percentage of zinc pyrithione mixed with the polyol and the addition ratio of the antimicrobial polyol mixture concentrate with the binder stream are selected to provide an overall concentration of zinc pyrithione in the binder of at least about 7500 ppm. The particles and binder are cured into a block and sliced to form carpet pad.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a Divisional Application of U.S. patent application Ser. No.10/840,309, filed May 6, 2004, entitled “Anti-Microbial Carpet Underlayand Method of Making,” which claims the benefit under 35 U.S.C. §119 ofU.S. provisional application Ser. No. 60/506,688 filed Sep. 26, 2003 andentitled “Anti-Microbial Carpet Pad and Method of Making,” both of whichare hereby incorporated herein by reference for all purposes.

FIELD OF THE INVENTION

This invention relates to antimicrobial rebonded carpet underlay andmore particularly to a method of making such underlay by mixing ananti-microbial agent in binder used to make the rebonded carpetunderlay.

BACKGROUND OF THE INVENTION

Carpet, especially wall-to-wall carpet, is normally installed with anunderlay, often in the form of a foam pad or cushion. Moisture, dirt,food particles, and other debris tend to filter through the carpet tothe pad. These conditions provide a breeding ground for various bacteriaand mold that may produce undesirable odors, cause degradation of thecarpet and/or pad, and/or contribute to a poor indoor air qualityenvironment for occupants of the premises.

A typical carpet pad consists of ground polyurethane foam particles of aspecific size range that are rebonded back together to form a continuousfoam pad of various densities and thickness. Typically, carpet padranges in density from four to eight pounds per cubic foot. Rebonded padis made from recycled polyurethane foam, typically from scraps of foamreclaimed from padding used in furniture, bedding, and automobileseating. The scraps are often of different sizes and colors. Therebonded foam is produced by grinding or chopping the scraps, mixing thechopped scraps with a binder, curing the binder, and slicing theresulting block of rebonded foam particles into a desired pad thickness.The binder may typically form ten percent of the weight of the finalrebonded pad. Various films or webs may be bonded to one or both sidesof the pad for various purposes.

SUMMARY OF THE INVENTION

A method of making antimicrobial rebonded carpet pad includes mixingzinc pyrithione with a polyol to form an antimicrobial polyol mixtureconcentrate, and blending the antimicrobial polyol mixture concentratewith a binder stream used to make rebonded carpet pad.

In an embodiment, the percentage of zinc pyrithione mixed with thepolyol and the addition ratio of the antimicrobial polyol mixtureconcentrate with the binder stream are selected to provide an overallconcentration of zinc pyrithione in the binder of at least about 7500ppm.

In one embodiment, an antimicrobial carpet underlay comprises a rebondedpad comprising particles of foam joined together with a binder preparedaccording the described method.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross sectional view of a carpet underlay according to oneembodiment of the present invention.

FIG. 2 is a block diagram of a binder mixing system used in makingrebonded pad for testing the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 is a cross sectional illustration of an antimicrobial carpetunderlay 10 which may be made according to one embodiment of the presentinvention. The underlay 10 includes a rebonded pad portion 12 includinga number of small pieces of foam 14 bonded together by binder 16. Thefoam pieces 14 may typically be ground or chopped scraps of polyurethanefoam used in making furniture. The underlay 10 may also include a film18 bonded to at least one surface of the pad 12, in this case the uppersurface of the pad 12. The film 18 is typically preferred to facilitatelaying carpet on top of the underlay 10 and for resisting the flow offluids into the pad 12, e.g. when fluids are spilled on carpet installedover the pad 12. A film 18 may also be laminated to the lower side ofthe pad 12 if desired. In the present invention, the carpet underlay 10is resistant to the growth of bacteria and mold on and within theunderlay 10. This antimicrobial resistance is achieved by adding aneffective amount of an antimicrobial compound to the pad 12 and/or tothe film 18, as described in more detail below.

In one embodiment, an effective biocide, or antimicrobial, compoundknown as zinc pyrithione (e.g. the material sold under the trademarkZINC OMADINE by Arch Chemicals Inc.) is incorporated into rebondedcarpet pad 12 by the following method. The chemical name for thiscompound is Bis(1-hydroxy-2(1H)-pyridinethionato-O,S)-(T-4)Zinc. Thezinc pyrithione in powdered form is mixed with a triol polyol of amolecular weight typically ranging from 3000 to 3500 to form a 20%strength antimicrobial/polyol mixture concentrate. Then, the 20%antimicrobial/polyol mixture concentrate is added to a binder stream ata 3.90% to 6.50% addition level to render a zinc pyrithioneconcentration of between 7500 to 12500 ppm in the binder 16. Theantimicrobial/polyol mixture concentrate and binder stream arepreferably held at between about 90 and about 100 degrees F. duringmixing and use. The binder 16 is typically composed of ⅓ aromatic oil, ⅓triol polyol, and ⅓ polymeric MDI. The binder is added to ground foamparticles, mixed together, compressed, injected with steam, and dried inthe form of a large block of rebonded foam particles. The block is thensliced into thicknesses suitable for carpet pad, e.g. three-eighth tofive-eighth inch, to produce the rebonded foam pad 12. The binder toground foam weight ratio is approximately 1:10. The final concentrationof Zinc Pyrithione in the rebonded pad 12 is therefore from about 750ppm to about 1250 ppm.

If desired, the particular concentration of zinc pyrithione in theantimicrobial/polyol mixture concentrate may be selected to be more orless than the 20% concentration used in this embodiment. The additionlevel of the antimicrobial/polyol mixture concentrate in the binder 16may then be adjusted to achieve a zinc pyrithione concentration of atleast about 7500 ppm and preferably between about 7500 to about 12500ppm in the binder 16.

If desired, a binder 16 to ground foam weight ratio of more or less than1:10 may be used. If other ratios are used, the particular concentrationof zinc pyrithione in the antimicrobial/polyol mixture concentrateand/or the addition level of the antimicrobial/polyol mixtureconcentrate in the binder 16 may then be adjusted to achieve a finalconcentration of Zinc Pyrithione in the rebonded pad 12 from about 750ppm to about 1250 ppm.

FIG. 2 illustrates a mixing system used in making binder 16 for testingthe present invention. A method for making binder 16 will be describedwith reference to FIG. 2. A mix tank 20 included a thirty-gallon drumand a vortex type mixer. Eighty pounds of polyol and twenty pounds ofpowdered zinc pyrithione were placed in tank 20 and mixed for at leastthree hours. A transfer pump 22 was used to pump the mixture from mixtank 20 to a run tank 24, which also includes a vortex mixer. Theantimicrobial/polyol mixture concentrate in the run tank 24 was mixedconstantly during production. If the mixer is turned off for anysignificant period of time, it should be restarted at least two hoursprior to use in production of rebonded pad 12.

During production of rebonded pad 12, a variable speed Watson Marlowpump 26 was used to flow the antimicrobial/polyol mixture concentratefrom the run tank 24 at a controllable rate. The rate is controlled by acontrol panel 28 and a variable frequency drive 30. The discharge sideof pump 26 is connected to the vacuum side of a binder pump 32. A tank34 of binder also has an outlet connected to the vacuum side of a binderpump 32. The discharge side of pump 32 is connected to a static mixer36. The outlet 38 of mixer 36 is coupled to a blender where polyurethaneparticles 14 are mixed with binder 16 to produce the finished rebondedpolyurethane pad 12.

During the operation of the system of FIG. 2, it is preferred that theantimicrobial/polyol mixture concentrate in the mix tank 20 and run tank24 be maintained at a temperature of between about 90 and about 100degrees F. during mixing and production operations. Likewise, the bindertank 34 is preferable maintained within the same temperature range.

It is sometimes desirable to include laminating film 18 on one or bothsurfaces of carpet pad 12. For example, such a film 18 may facilitatelaying and stretching of carpet by allowing the carpet to slide easilyon top of the pad 12 and avoiding undesirable movement or buckling ofthe pad 12. The film may also prevent fluids spilled on carpet frompenetrating into the pad 12. In one embodiment of the present invention,an antimicrobial laminating film 18 is laminated onto one or bothsurfaces of a carpet pad. The carpet pad may or may not include anantimicrobial compound as disclosed above.

The anti-microbial laminating film 18 of this embodiment inhibits thegrowth of certain bacteria and fungus when used in combination withprime polyurethane foam pad or rebonded polyurethane foam pad 12 ascarpet underlay. The anti-microbial film may be thermally laminated tothe top and/or bottom surfaces of prime polyurethane foam pad orre-bonded polyurethane flexible foam pad 12 where it acts as a barrierto inhibit the growth of microbes that accumulate on the surfaces ofcarpet underlay. This film 18 may also inhibit the growth ofmicroorganisms in other products where this film can be used as alamination barrier.

In this embodiment, a 0.45 to 0.50 mil monolayer blown film 18 includesbetween 500 and 1500 ppm of the antimicrobial compound zinc pyrithione(e.g. the material sold under the trademark ZINC OMADINE by ArchChemicals Inc.). The chemical name for this compound isBis(1-hydroxy-2(1H)-pyridinethionato-O,S)-(T-4)Zinc. The zinc pyrithionepowder is incorporated at 10% by weight into a LLDPE, linear low densitypolyethylene, resin concentrate supplied by PolyChem Alloy, Inc. underthe trademark POLYSEPT 554Z. The chemical description of the resinconcentrate is Mercaptopyridine-N-oxide in Polypropylene. This resinconcentrate has a specific melt index of 20 grams/10 mins. and 0.93density. About 1% to about 3% by weight of this concentrate is thenblended with a LLDPE/Copolymer resin mixture. Due to thermal breakdownof zinc pyrithione during processing of the film, the initial 10%concentration of zinc pyrithione in the concentrate may be effectivelyreduced to less than 6%. After mixing with the resin mixture andprocessing it into a film, the net effective concentration of zincpyrithione in the processed film is about 500 ppm to 1500 ppm. Suitablecopolymer resins may be EVA, EMA, or EMM. The copolymer resin consistsof approximately 60-70% by weight of the total mixture. The remainingmixture is 30-40% LLDPE by weight, including the 1-3% LLDPE concentratetreated with zinc pyrithione. The blended resins may then be extruded atbetween 450 and 550 degrees F. with a blow up ratio, i.e. bubblediameter to die diameter, of between 1.8 and 2.5:1. It is preferred thatthe extrusion temperature be kept below 500 degrees F. to minimizethermal breakdown of the zinc pyrithione.

It is apparent that zinc pyrithione powder may be incorporated at moreor less than 10% by weight into the resin concentrate. If other additionlevels are selected, the percentage of the concentrate blended with theLLDPE/Copolymer resin mixture may be adjusted to achieve a net effectiveconcentration of zinc pyrithione in the processed film of from about 500ppm to 1500 ppm.

The anti-microbial treated film may be thermally laminated (e.g. atabout 250-450 degrees F., 0.5 sec dwell time) to one or both sides of aprime polyurethane foam pad or rebonded pad 12 which may typically befrom about three-eighth inch to about five-eighth inch thick or otherdesired thickness. Other laminating methods may be used if desired, e.g.by use of an adhesive. The anti-microbial film may be laminated to ananti-microbial treated pad or non-anti-microbial treated pad. Theanti-microbial film may also be laminated to another anti-microbialtreated or untreated film for lamination to anti-microbial treated pador non-anti-microbial treated pad.

Biocidal effectiveness of the rebonded carpet pad 12 and/or film 18according the present invention may be determined by measuringinhibition of growth of bacterial and/or fungus using AATCC (AmericanAssociation of Textile Chemists and Colorists) 174, ASTM E2180-1, andASTM D 3273 test protocols compared to non-treated control standards.The AATCC 174 protocol was developed for determining the antimicrobialactivity of new carpet materials.

A number of specimens of carpet underlay 10 were made by methodsdescribed above, with various concentrations of zinc pyrithione in thebinder 16 and film 18 for testing to determine levels that provide aneffective antimicrobial effect. The specimens included a film 18 on oneside as illustrated in FIG. 1. This allowed testing of the foam side ofthe specimens to indicate antimicrobial effect of the pad 12 withoutfilm 18 and testing of the film side to indicate antimicrobial effect ofthe pad 12 with film 18. The AATCC 174 test method provides for testingboth unwashed and washed samples. Washed samples were treated accordingto the AATCC 138 protocol. The test results are summarized as follows.

The AATCC 174 test method includes three parts. Part I is a qualitativetest for antibacterial activity. Test specimens are placed into contactwith a nutrient agar which has been streaked with a bacterial culture.The specimens are then incubated. After incubation, a clear area ofinterrupted growth underneath and along the sides of the test specimenindicates antibacterial activity of the specimen. Standard strains ofbacteria are used, with Staphylococcus aureus and Klebsiella pneumoniaebeing the representative organisms.

In the AATCC 174, Part I tests various washed and unwashed specimenswere tested. An unwashed foam side specimen with 751 ppm of zincpyrithione passed the test with a one millimeter zone of inhibition forKlebsiella pneumoniae and a two millimeter zone of inhibition forStaphylococcus aureus. All unwashed and washed foam side specimens witha concentration of 1096 ppm or more of zinc pyrithione inhibited thegrowth of Klebsiella pneumoniae from underneath and along the sides ofthe specimen.

The AATCC 174, Part II test provides a quantitative procedure for theevaluation of the degree of antibacterial activity. Test specimens areinoculated with the test microorganisms. After incubation, the bacteriaare eluted from specimens by shaking in 100 milliliters of liquid. Thenumber of bacteria present in the liquid is determined and the percentreduction produced by the specimen is calculated.

In the AATCC 174, Part II tests, washed foam side specimens containing751 and 1096 ppm of zinc pyrithione provided a 90% reduction in thenumbers of both Staphylococcus aureus and Klebsiella pneumoniae. In allunwashed and washed film and foam side specimens containing aconcentration of 500 ppm or more of zinc pyrithione in the film and 1096ppm of zinc pyrithione in the pad, there was a reduction of at least 66%in Staphylococcus aureus with an average reduction of 92%.

The AATCC 174, Part III protocol provides a qualitative test forantifungal activity. Specimens are subjected to the growth of a commonfungus, Aspergillus niger, on Sabouraud Dextrose agar. Prewet specimensare inoculated and incubated at 28 degrees C. for seven days. Specimensare then assessed for growth of the fungus.

In the AATCC 174, Part III tests, washed and unwashed foam side sampleswith a concentration of 1096 ppm of zinc pyrithione in the pad producedno observable fungus growth. No growth was observed on washed andunwashed film side samples when the concentration of zinc pyrithione inthe film was 1500 ppm or greater.

Inhibitory mold activity was also tested by the ASTM E2180-01 testmethod. Good inhibitory activity for Aspergillus niger was observed whenfilm side specimens had a total minimum combined concentration of 1600ppm of zinc pyrithione. The total combined concentration is the sum ofthe concentration in the pad 12 of a specimen and the concentration inthe film 18 of the specimen. The tests indicate that a minimum of 500ppm may be preferred in the film 18, with a preferred complement minimumof 1100 ppm in the pad 12. Alternatively, a minimum concentration of 750ppm may be preferred in the pad 12 with a preferred complement minimumof 850 ppm in the film 18. Good results were achieved for some, but notall, specimens with a total combined concentration of 1251 ppm, i.e. 751ppm in the pad 12 and 500 ppm in the film 18. Therefore, the preferredminimum combined concentration is about 1600 ppm.

Mold susceptibility tests were also performed under the ASTM D3273 testmethod. No Aspergillus niger mold colonization was observed on film 18side specimens when the specimens had a total minimum combinedconcentration of about 1600 ppm zinc pyrithione. The tests indicate thata minimum of 500 ppm may be preferred in the film 18, with a preferredcomplement minimum of 1100 ppm in the pad 12. Alternatively, a minimumconcentration of 750 ppm may be preferred in the pad 12 with a preferredcomplement minimum of 850 ppm in the film 18.

The above described tests indicate that an effective antimicrobialcarpet underlay 10 can be made by incorporating 7500 to 12500 ppm ofzinc pyrithione into binder used to bind foam particles to make rebondedcarpet pad. The net concentration in the foam pad 12 is from 750 to 1250ppm of zinc pyrithione when the binder to foam weight is 1:10. Ifdifferent ratios of binder to foam are used, it is preferred to adjustthe concentration in the binder stream to achieve at least about 750 ppmof zinc pyrithione in the final foam pad 12.

The tests also indicate that an effective antimicrobial film can be madeby incorporating 500 to 1500 ppm of zinc pyrithione in the film 18. Asnoted above, the initial concentration is preferably adjusted to accountfor thermal degradation which occurs during film processing. Thus, theinitial ten percent concentration of zinc pyrithione in the resinconcentrate may be reduced to an effective five to six percent afterprocessing.

The tests also show that when both a foam pad 12 and a film 18 includinga biocide are combined to form a carpet underlay, lower concentrationsof zinc pyrithione may be used than may be necessary if only the pad 12or the film 18 contains the biocide. In general, in a carpet underlayhaving a biocide treated pad 12, but an untreated film 18, the pad 12preferably has a biocide concentration near the upper end of the rangetested, e.g. at least about 1100 to 1250 ppm of zinc pyrithione. For anunderlay having an untreated pad 12, and a treated film 18, the film 18preferably has a biocide concentration near the upper end of the rangetested, e.g. at least about 1100 to 1500 ppm of zinc pyrithione. Whenboth the pad 12 and film 18 are treated, it is preferred that thecombined concentrations for foam pad 12 and film 18 be at least about1600 ppm.

In the above disclosure, the concentrations of biocide in the foam pad12 and film 18 have been discussed in terms of ranges having a lowerlimit and an upper limit. It is apparent that it is preferred to includeconcentrations at or above the lower limits to achieve an effectiveantimicrobial activity in the products. That is, concentrations abovethe ranges tested should also be effective. Concentrations should bekept below a level at which the biocide may affect the mechanicalintegrity of the product. Since the biocide is a relatively high costpart of the product, normal practice should be to avoid using more ofthe biocide than is needed to achieve effective biocidal orantimicrobial activity.

The particular choice of an effective amount of the biocide also dependsupon the particular application in which the carpet pad will be used. Insome applications, there is a requirement that carpet products exhibiteffective antimicrobial activity after being washed. For thoseapplications, it may be desirable to use a concentration at or near theupper limits of the ranges given above. In the tests reported above, thespecimens at the upper ends of the ranges provided effectiveantimicrobial activity after washing. If the application does notrequire washing, a lower concentration of biocide provides an effectivebiocidal activity.

In the above description of making the rebonded foam pad 12, zincpyrithione was initially mixed in powder form with a polyol. Theresulting mixture is basically a suspension of particles in a liquid. Asnoted in the description of FIG. 2, it is desirable to continuouslyoperate a mixer in run tank 24 to insure that the zinc pyrithioneremains uniformly mixed with the polyol. It may be desirable to firstdissolve the zinc pyrithione in a fluid which is miscible with a polyol.Such a process is described in U.S. Pat. No. 5,114,984 issued to Branchet al. on May 19, 1992. In that patent, a pyrithione salt is dissolvedin an alkanolamine which is miscible with a polyol, which the Branchpatent indicates may then be used to make an antimicrobially effectivepolyurethane. Such a solution of zinc pyrithione in polyol may also besuitable for mixing with the binder described above for use in thepresent invention.

While the present invention has been disclosed in terms of specificstructures, chemical compositions and mixtures, and methods of makingcarpet underlay, it is apparent that various changes and substitutionsof materials and steps may be made within the scope of the presentinvention as defined by the appended claims.

1. A method for making rebonded carpet pad, comprising: mixing zincpyrithione with a polyol to form an antimicrobial polyol mixtureconcentrate, blending the antimicrobial polyol mixture concentrate witha binder stream, and selecting a percentage of zinc pyrithione mixedwith the polyol and an addition ratio of the antimicrobial polyolmixture concentrate with the binder stream to provide an overallconcentration of zinc pyrithione in the binder of at least about 7500ppm.
 2. The method for making rebonded carpet pad according to claim 1,further comprising: mixing zinc pyrithione with a triol polyol to a 20%strength antimicrobial polyol mixture concentrate, and blending the 20%strength antimicrobial polyol mixture concentrate with a binder streamat at least a 3.90% addition level.
 3. The method according to claim 2,further comprising blending the 20% strength antimicrobial polyolmixture concentrate with a binder stream at a 3.90% to 6.5% additionlevel.
 4. The method according to claim 1, further comprising: mixingthe binder with foam particles.
 5. The method according to claim 4,wherein the ratio of binder to foam particles is about 1:10 and resultsin an overall concentration of zinc pyrithione in the carpet pad of atleast about 750 ppm.
 6. The method according to claim 4, furthercomprising shaping the mixture of binder and foam particles into ablock, curing the binder and slicing the block to form carpet pad. 7.The method according to claim 6, further comprising laminating a film toat least one side of the carpet pad.
 8. The method according to claim 7,wherein the film comprises an effective amount of an anti-microbialcompound.
 9. A carpet underlay made by the method of claim
 6. 10. Acarpet underlay made by the method of claim 7.